fluid dispensing apparatus for dispensing small precise metered quantities of fluid, for example in a semiconductor manufacturing process, comprises two metering chambers disposed in series. Each metering chamber has an associated piston rod and fluid is dispensed therefrom alternately. Twice the volume of fluid is displaced from the upstream metering chamber so that when it dispenses fluid at the same time it can refill the second downstream metering chamber.
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1. Apparatus for dispensing metered amounts of a fluid, comprising: fluid supply means, an outlet and a fluid flow path between said supply and said outlet, wherein said fluid flow path comprises first and second metering ehambers disposed in series and associated with first and second pistons for dispensing fluid from said chambers, wherein a first of said metering chambers disposed closest to said fluid supply means displaces a volume of fluid twice that of said second metering chamber disposed closest to said outlet.
13. Apparatus for dispensing metered amounts of a fluid, comprising: fluid supply means, an outlet and a fluid flow path between said supply and said outlet, wherein said fluid flow path comprises first and second metering chambers disposed in series and wherein fluid is alternately dispensed from said first and second metering chambers, and wherein when fluid is dispensed from the first metering chamber closest to said fluid supply means, a part of the fluid dispensed from the first metering chamber is used to fill the second metering chamber.
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This invention relates to apparatus for dispensing fluids, and in particular to such apparatus for dispensing small precisely metered amounts of fluid. The invention is particularly useful for the supply of metered amounts of fluid such as silver epoxy in semi-conductor manufacturing processes, but is not limited thereto.
In a number of manufacturing processes it is necessary to be able to dispense very small precisely metered amounts of sometimes relatively viscous fluid. One example of such a manufacturing process is in the semiconductor industry in which small precise amounts of silver epoxy must be dispensed onto a substrate prior to die attachment. The silver epoxy may be dispensed in the form of dots or continuous beads on the substrate, the precise amount and pattern varying depending on the size of the die and the product being formed.
A large variety of different types of dispensing apparatus have been proposed for dispensing small precisely metered amounts of fluid in industries such as the semiconductor manufacturing industry.
In a typical dispensing system, a time-pressure control unit is used to dispense fluid from a syringe. Fluid in the syringe is dispensed by compressed air that is controlled by the time-pressure unit. The syringe is mounted on a moving assembly and to dispense a dot or a continuous bead the assembly moves to the desired position horizontally and then down to the desired level. Pressure is applied to dispense the liquid epoxy.
Other types of dispensing apparatus may be termed positive displacement apparatus and may be termed diaphragm type and piston type.
An example of a known diaphragm type apparatus is described in detail in U.S. Pat. No. 4,974,754 (Wirz). This apparatus includes a metering chamber defined by a diaphragm that is operatively connected to an actuating device. An inlet opening and an outlet opening to the metering chamber are opened and closed by the diaphragm in response to movement of the actuating device. Such diaphragm devices have a number of disadvantages, however, including the fact that in the operating cycle time must be provided for refilling the metering chamber between dispensing operations, the fact that limited amounts of fluid can be dispensed per cycle, and the fact that worn parts need to be replaced in order to maintain dispensing accuracy.
Another known device may be considered to be an example of a piston type device. In this device two piston chambers are provided which define metering chambers for the fluid being dispensed. Fluid is dispensed from each of these piston chambers in turn with a valve that is moved between two positions so as to alternately connect the two piston chambers to an outlet. This valve is often a rotary or a sliding valve. This has an advantage over the diaphragm type device in that one piston is refilled while the other is being dispensed, but there is still an idle time while the valve is being moved between positions. Furthermore the valve can leak and bubbles may be created in the fluid when the valve is moved between piston chambers.
According to the present invention there is provided apparatus for dispensing metered amounts of a fluid, comprising: fluid supply means, an outlet and a fluid flow path between said supply and said outlet, wherein said fluid flow path comprises first and second metering chambers disposed in series and associated with first and second pistons for dispensing fluid from said chambers, wherein a first of said metering chambers disposed closest to said fluid supply means displaces a volume of fluid twice that of said second metering chamber disposed closest to said outlet.
In a preferred embodiment the metering chambers are generally tubular and are of an identical length, and wherein the fluid may be dispensed from the metering chambers by the movement of the associated piston rods therein, the piston rod associated with the first metering chamber having a diameter greater than the diameter of the piston rod associated with the second metering chamber by a factor of 2. The piston rods may have an identical length of travel between a home position and a limit position so that they may be operated by a single actuator.
Preferably the pistons move out of phase with each other into and out of said metering chambers such that fluid is dispensed from the two metering chambers alternately.
In a particularly preferred embodiment the fluid flow path comprises three switch valves operable to interrupt the fluid flow path, a first switch valve being provided between the fluid supply means and the first metering chamber, a second switch valve being disposed between the first and second metering chambers, and a third switch valve being disposed between the second metering chamber and the outlet.
In this arrangement, when the first and third switch valves are open and the second switch valve is closed, fluid is allowed to flow into the first metering chamber to fill the first metering chamber and at the same time fluid is dispensed from the second metering chamber to the outlet. When the first switch valve is closed and the second and third switch valves are open, half of the fluid in the first metering chamber is dispensed from the first metering chamber to the outlet and the other half of the fluid in the first metering chamber is used to fill the second metering chamber.
The apparatus may comprise a main body portion formed of two halves, with the fluid flow path being formed in one of the halves and the two halves being joined at an interface, and the three switch valves all being formed at the interface. A diaphragm may be located between the body portion halves, and means may be provided at the switch valves to urge the diaphragm into positions to open and close the fluid flow path.
According to another aspect of the present invention there is provided apparatus for dispensing metered amounts of a fluid, comprising: fluid supply means, an outlet and a fluid flow path between said supply and said outlet, wherein said fluid flow path comprises first and second metering chambers disposed in series and wherein fluid is alternately dispensed from said first and second metering chambers, and wherein when fluid is dispensed from the first metering chamber closest to said fluid supply means, a part of the fluid dispensed from the first metering chamber is used to fill the second metering chamber.
An embodiment of the invention will now be described by way of example and with reference to the accompanying drawings, in which
Referring firstly to
Each piston is adapted to reciprocate between a position in which the piston rod is at one extreme position in which the rod is not within the chamber (or at least not substantially within the chamber), and a limit position at which the piston rod is substantially within the chamber. It should be noted here that both pistons have the same length of travel, ie the distance between the home and limit positions, and can therefore be controlled by the same actuator. However, as will be explained below, it is necessary for the upper chamber to displace twice the volume of fluid compared to the lower chamber. Since the length of the two chambers must be the same for the pistons to have the same length of travel (which is preferable as will be explained below), this difference in volume of fluid displaced comes from a difference in the diameter of the piston rods associated with the two chambers and in particular the diameter of the piston rod associated with the upper chamber must be greater than the diameter of the piston rod associated with the lower chamber by a factor of 2.
Referring now to
At the interface between main body parts 1a, 1b where the locations 20a-c are to be found is provided a diaphragm 21 that covers locations 20a-c. Diaphragm 21 may be located in a recessed area 22 of main body part 1a. Formed in main body part 1b at positions corresponding to locations 20a-c are three valves 23,24,25. Valve 23 is positioned at location 20a and is an inlet valve. Valve 24 is positioned at location 20b and is an intermediate valve, while valve 25 is an outlet valve and is positioned at location 20c. Each valve 23-25 is formed with a part spherical end surface 26 that corresponds to a part spherical surface formed in the dispensing path at locations 20a-c. It will be understood that the valves 23-25 may be operated to force the diaphragm 21 into the respective locations 20a-c to close off the dispensing path. Valves 23-25 are operated by pneumatic actuators not shown in the drawings.
The operation of the dispensing apparatus of this embodiment will now be described with particular reference to
The third stage shown in
The skilled reader will appreciate that the present invention provides a number of advantages over the prior art. Firstly, idle time is minimized. Since one chamber is refilled while the other is used to dispense fluid, no time is wasted while waiting for a chamber to be filled. In contrast to prior piston designs, there is no sliding or rotary valve that needs to be physically moved to change between dispensing pistons and which causes delay in prior art piston type designs. Instead the valves 23-25 can be switched between open and closed conditions almost immediately. Indeed while described herein as valves since they function to control fluid flow, they may also be considered as switches that operate almost instantaneously. The absence of a sliding or rotary valve avoids the danger of bubbles being introduced into the fluid and avoids the danger of leakage at the valve. The possibility of leakage can further be limited if the piston rods are formed to slightly thinner than the diameter of the piston chambers so as not to slide against the walls of the piston chambers.
In contrast to the diaphragm design of Wirz, the metering chambers are defined by the piston chambers and are therefore of a reliable and repeatable size that will not change with wear.
A further important advantage of the present invention is that it comprises a continuous flow system with no dead volume. In the prior art designs dead volumes exist in which fluid may accumulate and potentially harden because there is no continuous flow of fluid. timing while shifting each value by an amount as much as one delay element is suiotably used. The delay means can output the tap coeffients by a simple construction using the delay elements.
The synthesizing means of the transversal filter is synthesizing means having multiplying circuits of the same number as that of sampling values and an adding circuit for adding outputs from the multiplying circuits. As a multiplying circuit, a multiplying circuit having impendances which are connected in parallel and to which the inputted sampling value is dividedly supplied, switches each of which is connected to each impendance in series and which opens or closes by a value of each bit constructing the inputted tap coefficient, an amplifier to which outputs from the switches are supplied, and a feedback impendance for feeding back an output of the amplifier is suitably used. The synthesizing means can weight the sampling value with the tap coefficient to synthesize them by a simple construction using the impendances, switches, and feedback amplifier.
According to the present invention, there is provided a receiver having an A/D converter for converting an output from the transversal filter to a digital signal and a program section for realizing functions fo the demodulating units. Since it can be applicable to a plurality of communication systems without having a band pass filter every communication systems, a circuit scale can be reduced.
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